console, serial: multiple cleanups

[00xc]

• serial: make SerialPort fields private and use SerialPort::new() where needed.
• serial: add SerialPort::{inb, outb}() to simplify code.
• console: remove Option from Console, as it is always Some.
• console: initialize WRITER directly from init_console()
• console: return error from install_console_logger() instead of implicitly panicking.